There has been conventionally used an imaging apparatus that generates images of the same subject that have different exposure times, and synthesizes these images into one image. The image synthesized in this manner is referred to as a high dynamic range (HDR) image. By the imaging apparatus that generates this HDR image, the generation of an image without defects such as so-called blown out highlights and blocked up shadows can be performed in image capturing of a subject having a wide dynamic range, as in the case of performing shooting of a person in a backlight state. In such an imaging apparatus, an HDR image is generated by the synthesis of an image signal with a long exposure time and an image signal with a short exposure time, and a noise of this HDR image is estimated. Then, processing for achieving improvement in image quality of the HDR image is performed on the basis of the estimated noise. For example, values obtained by multiplying square roots of the image signals obtained before synthesis, by a predetermined constant are estimated as noises of these image signals. Then, there is proposed a system that estimates, as a noise of an HDR image, a value obtained by synthesizing a plurality of noise estimate values that have been estimated in the above-described manner, on the basis of a synthesis ratio in HDR synthesis (e.g., refer to Patent Literature 1.).